The objective of this reseach will be to learn something of the nature of the 'pantothenic acid' content of blood which is determined by microbiological assay with Lactobacillus plantarum (arabinosus) without prior enzymatic treatment. Some evidence had been previously obtained that the 'pantothenic acid' of blood is present as a protein-pantothenate complex that is not dialyzable (and consequently not filterable at the kidney glomerulus). Other results indicated that the 'pantothenic acid' of blood, as determined without enzyme treatment, is not present as coenzyme A or acyl carrier protein. Following characterization of the 'pantothenic acid' of blood, physiological experiments will be undertaken to learn something of the significance of the 'pantothenic acid' in the transport and metabolism of the vitamin.